The present invention has numerous applications. However, for purposes of the present specification, the invention will be described in conjunction with the simultaneous drilling of a series of printed circuit boards.
In the manufacture of printed circuit boards, one operation includes that of drilling a number of holes in the circuit board at specified points. These holes will receive the electrical leads from various electrical components to be assembled on the board. Usually, a plurality of boards are simultaneously drilled in accord with a master positive film defining the specific locations of the drill holes. Towards this end, a work surface is mounted to a base frame for movement in fore and aft and sidewise directions; that is, along the directions of an orthagonal coordinate system. All of the boards on the work surface can thus be positioned simultaneously and by providing a multiple drill head, a first set of holes in a specific position on each board can be simultaneously drilled.
When a large number of boards are drilled simultaneously, the multiple drill head is necessarily elongated to accommodate a series of drills in side-by-side relationship. In order that all of the holes be as identical as possible in the respective boards, it is desirable that the elongated multiple drill head itself be brought down towards the work in such a manner that the respective drills move through precisely the same distances. Towards this end, it is necessary that the opposite end portions of the elongated head move equal distances toward the work.
The foregoing desired operation can pose certain mechanical problems in the mounting of the drill head for such movement. Normally, a pair of spaced parallel rails normal to the work surface are provided for guiding opposite end portions of the elongated head towards the work. However, the absolute straightness and parallel relationship of the rails cannot always be maintained and when the rails are bridged by a relatively long drill head member, twisting or canting may occur which will result in the undesirable movement of one end portion of the drill head member ahead or behind the other so that all of the drills do not engage the various circuit boards simultaneously.